The geochemistry of methane in Lake Fryxell, an amictic, permanently ice-covered, antarctic lake

Abstract

Abstract. The abundance and distribution of dissolved CH 4 were determined from [1987][1988][1989][1990] in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement is controlled by diffusion. CH 4 concentrations were <1 uM in the upper oxic waters, but increased below the oxycline to 936 uM at 18 m. Sediment CH 4 was 1100 #mol (1 sed) -1 in the 0-5 cm zone. Upward flux from the sediment was the source of the CH, NH + , and DOC in the water column; CH 4 was 27% of the DOC + CH 4 carbon at 18 m. Incubations with surficial sediments indicated that H 14 CO3 reduction was 0.4 Mmol (I sed) -' day-' or 4x the rate of acetate fermentation to CH 4 . There was no measurable CH 4 production in the water column. However, depth profiles of CH 4 , NH + , and DIC normalized to bottom water concentrations demonstrated that a significant CH 4 sink was evident in the anoxic, sulfate-containing zone of the water column (10-18 m). The 6' 3 CH 4 in this zone decreased from -72 /o at 18 m to -76 /oo at 12 m, indicating that the consumption mechanism did not result in an isotopic enrichment of 13 CH 4 . In contrast, 6' 3 CH 4 increased to -55 %o at 9 m due to aerobic oxidation, though this was a minor aspect of the CH 4 cycle. The water column CH 4 profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic CH 4 consumption was 0.012 yr -1 . On a total carbon basis, CH 4 consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments and serves to exemplify the importance of CH 4 to carbon cycling in Lake Fryxell.

Dissolved gas dynamics in perennially ice‐covered Lake Fryxell, Antarctica

“…Financial support was provided by the National Science Foundation grants DPP 91-18363 and OCE 93-02812. the lakes provide model environments in which to study the biogeochemical cycles of carbon, methane, and sulfur in aquatic systems (Smith et al 1993). However, the physical limnology of the lake, which impinges on the hydrological balances as well as the biogeochemical cycles, is not well understood.…”

Biogeochemistry of methane in the permanently ice-covered Lake Untersee, central Dronning Maud Land, East Antarctica

“…Such lakes serve as unique model systems for estimating the role of CH 4 in periglacial lacustrine environments during former glacial periods and for evaluating the importance of microbial biogeochemical processes in low-temperature aquatic ecosystems. In contrast with the polar regions of the Northern Hemisphere, there are only a few detailed studies on the occurrence and biogeochemistry of CH 4 in Antarctic lakes and ponds (e.g., Franzmann et al 1991;Smith et al 1993;Galchenko 1994).…”

Evidence of deep circulation in two perennially ice‐covered Antarctic lakes

“…Such profiles were used by Lawrence and Hendy (1985) to infer a stratified refilling period in the lake's history beginning -1,200 years ago. The water-column temperature increases from 0.4"C at the ice-water interface to 3.4"C between 9 and 10.5 m and then decreases to 2.6"C at the lake bottom (Smith et al 1993;Miller and Aiken 1996). Fluid densities calculated by Aiken et al (1991) show that the water column was density-stable during the summer sampling of 1987.…”

“…Smith et al (1993) reported that fluid electrical conductivity increased with depth and that gradients in salinity remained constant from one season to the next. Solute concentration increased significantly beginning at -6 m and appeared to be diffusionally controlled (Smith et al 1993).…”

“…Smith et al (1993) reported that fluid electrical conductivity increased with depth and that gradients in salinity remained constant from one season to the next. Solute concentration increased significantly beginning at -6 m and appeared to be diffusionally controlled (Smith et al 1993). Such profiles were used by Lawrence and Hendy (1985) to infer a stratified refilling period in the lake's history beginning -1,200 years ago.…”